Methylene chloride (dichloromethane) has been employed in recent years as a vapor pressure depressant and co-solvent for the pressurizing gases and formulation ingredients in aerosol applications. The presence of aluminum and other alloying metals in the filling equipment and in the aerosol containers has made it necessary to provide stabilizers to prevent attack on the metals and degradation of the solvent. In some applications in which aqueous systems are pressurized for use in aerosol containers, the containers are frequently made of tin-plated steel. Chlorinated solvents, and especially methylene chloride are subject to hydrolysis and degradation and attack the tin plate under such conditions. This property has hindered their use in aqueous aerosols due to the resultant container corrosion. By adding certain inhibiting agents to the chlorinated solvents the corrosive behavior in solvent/water aerosols can be minimized.
A rather significant market exists for aerosols containing water. Incorporation of chlorinated solvents in many of these formulations produce desirable performance properties otherwise absent. Water-containing aerosols many times have solubility problems with active ingredients which are helped by the presence of chlorinated solvents. The chlorinated solvents are also compatible with the hydrocarbon propellants and can be used in partial substitution for these. Water-based aerosols dry quite slowly compared to anhydrous systems and incorporation of methylene chloride enhances the evaporation.